The invention relates to a radiation-emitting semiconductor diode comprising a semiconductor body with a semiconductor substrate of a first conductivity type on which are at least present in that order a lower cladding layer of the first conductivity type, an active layer, and an upper cladding layer of a second conductivity type, the active layer and at least one of the cladding layers, to be called first cladding layer hereinafter, comprising mutually differing semiconductor materials which each comprise a mixed crystal of at least two binary compounds with two sub-lattices, atoms of different elements being present side by side on at least one of the sub-lattices, which is to be called first sub-lattice hereinafter. The invention also relates to a method of manufacturing a radiation-emitting semiconductor diode, whereby are provided on a semiconductor substrate of a first conductivity type in that order at least a lower cladding layer of the first conductivity type, an active layer, and an upper cladding layer of a second conductivity type, mutually differing semiconductor materials being chosen for the active layer and for at least one of the cladding layers, which is to be called first cladding layer hereinafter, each of the said semiconductor materials comprising a mixed crystal of at least two binary compounds and having two sub-lattices, atoms of different elements being provided on at least one sub-lattice, which is to be called first sub-lattice hereinafter.
Such radiation-emitting diodes, especially when the wavelength of the emission lies in the visible range of the spectrum, are suitable radiation sources--provided they are constructed as lasers --for inter alia information processing systems such as laser printers with which information is written, optical disc systems such as Compact Disc (Video) (CD(V)) players or bar code readers, by which information is read, and Digital Optical Recording (DOR) systems, by which information is written and read. Numerous applications are also possible in opto-electronic systems for LED versions of such diodes.
Such a radiation-emitting diode and such a method of manufacturing same are known from the article "AlGaInP Double Heterostructure Visible-Light Laser Diodes with a GaInP Active Layer Grown by Metalorganic Vapor Phase Epitaxy" by K. Kobayashi et al., published in IEEE Journal of Quantum Electronics, vol. QE-23, No. 6, June 1987, p. 704. This article describes a radiation-emitting semiconductor diode comprising an active layer situated on a substrate of n-type GaAs between two cladding layers. The active layer and the first cladding layer, both cladding layers in this case, comprise mutually differing semiconductor materials, in this case InGaP and InAlGaP, respectively, which each comprise a mixed crystal of at least two binary compounds, in this case exactly two for the active layer and three for the first cladding layer, namely InP, AlP, and GaP, and having the sub-lattices, i.e. two f.c.c. lattices, in which the atoms forming the binary compounds are present, here In, Al, and Ga atoms on the one hand and P atoms on the other hand, while atoms of different elements, in this case In and Ga atoms for the active layer and In, Al, and Ga atoms for the first cladding layer, are present side by side on at least one of the sub-lattices, in this case the sub-lattice on which In, Al and Ga atoms are present. In the radiation-emitting diode, which is constructed as a laser here, there is a strip-shaped region which acts as a resonance cavity and inside which electromagnetic radiation can be generated by the pn-junction present in the active InGaP layer when current is passing in the forward bias direction. The known diode lasers are manufactured at a growing temperature of 700.degree. C. or lower and comprise a gallium arsenide buffer layer. The emission wavelength of the diode constructed as a laser in this case is approximately 670 nm (i.e. the wavelength in photoluminescence is approximately 660 nm, which corresponds to a bandgap of approximately 1,88 eV; it will be recognized that in this specification the European notation for a decimal point, namely a comma, is used).
A disadvantage of the known semiconductor diode laser is that its maximum operating temperature is comparatively low. This depends inter alia on the temperature dependence of the starting current. The starting current (I) is related to the temperature (T) in the following way: I/I.sub.o =exp((T+.DELTA.T)/T.sub.o), where I.sub.o is the starting current at 0.degree. C., T the temperature of the heatsink, .DELTA.T the temperature rise in the active region, and T.sub.o the so-called characteristic temperature. This is typically 75 up to a maximum 90 K for the known diode laser in the temperature range from 30.degree. to 60.degree. C., whereas, for example, the T.sub.o value may be as much as 150 K for a GaAs/AlGaAs laser, which implies a much smaller increase in the starting current with rising temperature. The value of T.sub.o is directly related to optical and electrical losses inside the laser resonance cavity and may be increased in that the difference in bandgap between the active layer and one or both cladding layers is increased. This may be achieved, for example, by increasing the aluminum content of the cladding layers, but this is less effective because of the indirect nature of these layers, and it is more difficult then to dope the cladding layers, especially the p-type cladding layer, sufficiently strongly.